Bogus error "'visibility' attribute takes one argument" in C++03 mode only

[Quuxplusone]

https://godbolt.org/z/bMoKTsc38

struct [[gnu::visibility("default")]] S {};

Clang 17 introduced the ability to parse C++11-style [[attributes]] even in C++98 mode.
Compile the line above with -std=c++11 and it compiles fine.
But compile it with -std=c++03 and you get a bogus error:

<source>:1:10: error: 'visibility' attribute takes one argument
    1 | struct [[gnu::visibility("default")]] S {};
      |          ^

There is one argument there! So Clang shouldn't be complaining, should it?

[Quuxplusone]

Fixed by b873847!